Amplification system



June 17, 1941. w. SOLLER AMPLIFICATION SYSTEM Filed Dec.

10 Sheets-Sheet 5 I I I INVENTOR. wuf/lw jam/a,

BY O AT TORNEY 7 June 17, 1941.

W. SOLLER AMPLIFICATION SYSTEM Filed Dec. 5, 1938 10 Sheets-Sheet 6 70 Pan H? PACK v tri 7'0P0WE1? PA ck IN VEN TOR. 50%,

June 17, 1941. w. SOLLER AMPLIFICATION SYSTEM 10 Sheets-Sheet 7 Fil ed Dec. 5, 1938 :E; EI 1 8 INVENTOR. WAY/Eva (Sn/660v 7 Y Q AI-TORNEY I III we W. SOLLER AMPLIFICATION SYSTEM June 17, 1941.

A Fiied Dec. 5, 1938 10 Sheets-Sheet a 'Z IEMEU .ra Rowe- PAC/r INVEN TOR v Wafiw z 4 Ira-E ATTORNEY W. SOLLER AMPALIIFICATION SYSTEM June 17, 1941'.

Filed Dec. 5, 193a -10 SFe'ts-Sheet 9 INV NTOR 05654 BY A.

W ATTORNEY.

June "17, 1941. w. SQLLER 2,245,616

I YAMPLIFICATION SYSTEM Fi -led Dec. 5; 1938 10 Sheets-Sheet 1o 4 INVENTOR.

. Pf/45am SaZ/Q 1 dag 6.

ATTORNEY Patented June 17, 1941 AMPLIFICATION SYSTEM Walter Seller, Cincinnati, Ohio, assignor of onehalf to William H. Woodin, Jr., Tucson, Ariz.

Application December 5, 1938, Serial No. 244,123

14 Claims.

My invention relates broadly to electron tube amplification systems and more particularly to a balanced circuit arrangement for electron tube amplifiers.

This application is a continuation-in-part of my application Serial No. 732,170, filed June 23, 1934, for Balanced electron tube amplifier, now Patent 2,166,184, granted July 18, 1939.

One of the objects of my invention is to provide rangement embodying the power source balancing principle of my invention; Fig. 2 shows a modified circuit arrangement embodying this principle; Fig. 3 shows a coupling system for multiple electrode tubes arranged in accordance with my invention; Fig. 4 illustrates the application of my invention to three electrode electron tubes of twin arrangement; Fig. 5 is a circuit arrangement showing the application of my invention to electron tubes of the twin pentode type; Fig. 6 is a modified circuit arrangement illustrating the application of my invention in coupling multiple electrode electron tubes while maintaining stabilized operation of the tubes; Fig. 7 shows a cascade schematic circuit arrangement for tubes of the class illustrated in Fig. 1; Fig, 8 shows a circuit arrangement embodying the dual compensating principle of my invention, that of compensating for-power source and cathode emission change; Fig. 9 illustrates a modified form of ba1- ance circuit embodying my invention; Fig. 9a is a fragmentary diagram illustrating the character of cathode control which may be used in the balance system of my invention; Fig. 10 illustrates the application of a tube of the class illustrated in Fig. 2 applied to the balancing mesh circuit oi Figs. 8 and 9; Fig. 11 illustrates the application of a balance circuit operating in accordance with my invention to tubes of the class illustrated in Fig. 1;

a balancing circuit for four and five element elecm Fig. 12 shows the balance circuit of my invention tron tube amplification systems having a high de employed in connection with a double anode gree of stability. screen grid tube; Fig. 13 shows the balanced am- Another object of my invention is to provide a plifier system of my invention using tubes of the circuit arrangement for multiple electrode twin class illustrated in Fig. 8 in cascade arrangetubes for amplification of electric currents under ment; Fig. 14 shows a cascade circuit arrangeconditions of high stability. ment illustrating dual compensation with Fig. 1 Still another object of my invention is to protype of circuit; Fig. 15 illustrates the balancing vide a circuit arrangement for amplification sysarrangement for the individual stages applied to tems in which a high degree of amplification may a cascade circuit employing a tube of the class be effected while maintaining the operation of the illustrated in Fig, 10 in the first stage and a twin circuits in highly stabilized condition and balanctriode in the second stage; Fig. 16 illustrates a ing the circuit by use of an auxiliary electrode balancing mesh circuit constructed in accordintroduced into the electrode assembly of the tube ance with my invention and employing indirectly with the circuit so arranged that the algebraic sum heated tubes and independently balanced circuits of the instantaneous voltage values in different associated therewith; Fig. 17 shows afurther casparts of the circuit is zero in the balanced condicade system embodying my invention applied to tion of the circuit. indirectly heated tubes with resistance mesh cir- Other and further objects of my invention recuits for balancing the separate stages independside in the production of a circuit arrangement ently; Fig. 18 illustrates the application of the for an electron tube amplification system as set principles of my invention to a tube circuit havforth more fully in the specification hereinafter ing a four-resistance balancing mesh and infollowing by reference to the accompanying drawvolving the currents from three electrodes of the ings, in which: tube; Fig. 19 shows a modified arrangement of Fig. 1 diagrammatically shows a circuit aradjustable mesh which may be employed in the tube circuit of Fig. 18; Fig. 20 shows a balanced circuit arrangement employing a dual functioning tube applied to the circuit of Fig. 18 Fig. 21 illustrat'es the application of the type of tube illustrated in Fig. 3 to a modified form of a resistance mesh; Fig. 22 shows the manner of cascading modified tube arrangements in a modified cascade circuit; Fig. 23 illustrates a cascade system embodying the principles of my invention in which four-resistance balancing meshes are employed in both stages; Fig. 24 illustrates a dual functioning first-stage tube with a four-resistance balancing mesh circuit coupled to a double auxiliary anode tube second-stage, also balanced with a four-resistance mesh; Fig. 25 shows the balancing circuit of my invention applied to a tube in which a different source is used for the plate and screen grid as distinguished from the source used for the filament or heater element; Fig. 26 shows a modified resistance mesh circuit used for a tube including a screen grid and a shield grid where separate sources are used for the plate and screen grid as distinguished from the source used for the filament or heater; Fig, 27 illustrates the application of the principles of my invention to a. tube employing, in addition to control, screen and suppressor grids, a space charge grid, an anode and a filament where the plate and screen grid voltages are held constant while the emission of the filament is held constant by use of an independent source; Fig. 28 shows a circuit embodying the principles as set forth in the circuit of Fig. 27 but illustrating a heater type tube instead of a directly emitting cathode; and Fig. 29 shows a modified circuit for a tube similar to Fig. 27.

Referring to the drawings in detail, reference character l, in Fig. 1, designates a three electrode electron tube including cathode 2, control grid 3 and anode l with an auxiliary anode 5 included in the tube. tively low potential impressed thereon and serves as a means for preventing oscillation and stabilizing the operation of the amplifier circuit. The power supply circuit for energizing the circuits of the electron tube I is connected across terminals 6. A series circuit extends from terminals 6 through resistor i and adjustable resistors 8 and 23 to the cathode 2 as shown. Another series path extends from anode 4 through adjustable resistor 9 to the positive side of the potential source at one of the terminals 5. The input circuit tothe tube is indicated at iii connected at one side to control grid 3 and at the other side through resistor l to the cathode 2. The output circuit is shown at l I connected at one side to auxiliary anode 5 and at the opposite side to a point l2 be tween adjustable resistors 8 and 23. A resistor M is connected at one end to high potential point and at the other end to the auxiliary anode 5. The drop in potential across resistor 14 is impressed on auxiliary anode 5 for effecting balanced operation of the circuit The input circuit may be regulated by placing a regulating resistance across the input circuit it). Meters may be arranged in series with the power supply circuit and shunted across the output of each stage for adjusting the balanced relation of the several circuits. The cir cuits of the meters shunted across the output are opened during o eration. Balance of any one stage can be made by the meter in the output of the following stage, thus obtaining the balance with actual operating conditions. The auxiliary anode 5 is electronically coupled with the electrodes 2, 3 and Q. Resistors i, 8, 9, l4 and 23 are determined to give the preferred characteristics and best operation conditions. When adjustments for balance and compensation for voltage changes are made the input is turned ofi". The grid bias from the voltage drop in l is obtained by a closed path in the input circuit. The final adjustment for balance and compensation for changes in the power source are made by adjusting 8, 5 and Hi. In Fig. 7 I have shown how tube circuits of the class shown in Fig. 1 may be cascaded. I have shown in the second stage similar elements to those described with prime designations added to the reference characters.

In Fig. 2 I have illustrated the same arrangement of resistors in circuit with the electrodes of the tube, but in this instance I employ a gridlike anode l5 interposed between the cathode and the control grid 3 and anode 4 and directly in the electron discharge path, The output circuit is similar to the arrangement of the output cir- The auxiliary anode 5 has a relacuit in the system of Fig. 1. The balancing is effected in the same way that the balancing is obtained in the system of Fig. l. The particular advantage of the circuit of Fig. 2 is that the output is taken from points of very low D. C. potential.

By applying the principles of my invention to multi-stage amplifier systems, a circuit arrangement of the type illustrated in Fig. 3 is secured. I have shown the coupled system employing a pentode in which there is introduced in addition to the electrodes illustrated in Fig. l, the suppressor grid H and the screen grid E8. The second tube of the coupled system is indicated at l and contains electrodes similar to the electrodes of tube I and are correspondingly numbered with a prime character as shown. The power supply circuit for the multi-stage system is shown generally by a source l9 connected through adjustable regulating resistance to the series circuit extending from terminal 21 through adjustable resistor 22 to adjustable resistor 8 and thence through adjustable resistor 23 to the cathode 2 through adjustable resistor I, returning to the source i9. Resistor 79 which shunts the cathode 2 enables less current to be used by the filament in the first stage than in the second and takes care of the current through resistor 22 not passing through the filament of the second stage. Similar use is made of resistor l9 in Figs. 6 and '7, and of resistor 59 in Fig. 13, for example. Suppressor grid ll connects to the cathode circuit as indicated at 24. Screen grid 18 connects to a point in the power supply circuit as indicated at 26 through adjustable resistor 5'2. Adjustable resistor 9 is included between anode 4 and point in the series circuit. The coupling resistor 14 connects between high potential point l5 and the auxiliary anode 5 of tube l. The circuit of my invention allows paralleling of the two stages and therefore a lower potential power supply may be used. The complete load of the plate circuit is also utilized. The auxiliary anode 5 serves as the balancing means in cooperation with the adjustable resistors and the regulated input at It. The circuit of the second tube I is similar to the circuit of tube I. A connection extends from one end of resistor M to control grid 3'. The suppressor grid 11' connects to the cathode circuit of cathode 2 as indicated at 24. The screen grid 58 connects to terminal 25' in the output circuit through resistor 52. Auxiliary anode 5 connects to one end of resistor 14 while anode 4' connects to the other end of resistor M as indicated at l5. The preferred characteristics and operating conditions are more flexible with a pentode in that the additional resistance 52 can be adjusted and with a coupled circuit the relative voltage on the two stages can be regulated by resistor 22. The preferred characteristics, balance and compensation for power source changes are obtained in a manner similar to that stated for Fig. 1.

In Fig. 4 I have shown the principles of my invention applied to twin triode tubes indicated at 21 and 21'. Each of these tubes contains a cathode shown at 28 and 28' heated by filaments 29 and 25', respectively. The heating filaments 29 and 29' are energized by the same power source as that indicated at D. C. The tubes contain control grids 30 and 3| and 30 and 3|, respectively. The tubes contain anodes 32 and 3 3 and 32' and 33', respectively. Separate input circuits are provided for the control grids 30 and 3| of tube 2'! as represented at 34 and 35, I'espe to point 4| in circuit with cathode 23.

the required potential for the plate supply system of tube 21. Anodes 32 and 33 are connected to opposite ends of coupling resistor M and to the high potential point l5 which connects through adjustable resistor 9 to point 26 in the power supply circuit. The additional anode functions simultaneously to eifect amplification, balance and compensation of power source changes. When the same input is placed on both 34 and the combined amplification of both sides of the tube is obtained on the input of the second stage. When two inputs are being impressed they are combined on the second stage. In this circuit twin tubes function as twin tube amplifiers and simultaneously'bal'ance out voltage variations. The preferred characteristics, balance and compensation are obtained in a manner similar to that stated for Fig, 1.

The elements in the second stage of amplification constituted by tube 21' are arranged simi larly to the arrangement of elements and the circuits therefor illustrated in connection with tube 2'! except that control grids 30' and 3| are connected together and to one end of coupling resistor l4. Anodes 32' and 33' connect across opposite ends of resistor l4 and to high potential point 15' as shown.- The balancing and compensating condition is obtained similarly to that of the first stage. i

Fig. 5 illustrates theapplication of the principles of my invention to twin pentode tubes shown at 36 and 3E. The twin pentode tubes have in addition to the elements illustrated in Fig. 4, suppressor grids 31 and 38 and screen grids 39 and 40. Similarly, tube 33' includes suppressor grids 31' and 38 and screen grids 39 and 40. The external circuit arrangement'is similar to the circuit described in connection with Fig. 4. It will be seen that the suppressor grids 31 and 38 connect to the point 4! in the cathode circuit which contains cathode 28. Similarly, suppressor grids 31 and 38 connect Separate adjustable resistors 46 and '41 are disposed in the conductors leading to screen grids 39 and 40 for tube 36 from'point 42 in the output circuit and in the case of tube 36', adjustable tap resistors 45' and 4'! are included in the conductors leading to screen grids 39 and 43' from point 42 in the output circuit. Resistances Q6 and 41 are placed in the circuit to obtain the correct potentials on grids 39 and 49. Resistors 23 and 8 are separate variable resistances, 23 functioning to change the tube circuit characteristics and 8 functioning directly to adjust for balance. The circuits are balanced and a high degree of stability is obtained in the system of Fig. 5 by adjustment of resistors 823-22-%41 and 8'2348'-4'i' to those values which give the preferred characteristics of the tubeand circuit for balance and best operation. That is to say, the characteristics of stage one are changed by adjusting 23, 1, 46, and 22. When thepreferred characteristics are obtained then 8, 9 and [4 are adjusted until a constant grid bias on the second stage is maintained when the voltage of the power source changes. The second stage or in general the last stage is then adjusted for bal ance in thehusual way for 'zero potential across the output when zero potential is across; the input. In this circuit twin pentodes are used in place of the twin triodes shown in Fig. 4, the corresponding elements being connected in this circuit. in exactly the same Way.v The suppressor and screen grids do .not enter into the balancing part of the circuit but thescreen grid voltage-control resistors 41, 46, 41' and 46 give this circuit additional flexibility to obtain preferred characteristics and operating conditions. The balance and compensation are obtained in a manner similar to that for Fig. 4.

My invention is applicable to coupling circuits for. multiple electrode tubes generally as indi- 'cated in Fig. 6. A tube circuit similar to the circuit'of Fig. 2 has been illustrated where eachv tube 44 and 44' has a screen grid in place of the space charge grid, and includes'in addition; to the electrodes illustrated in connection with the circuit of Fig, 2, a suppressor grid I1 and II, respectively. Suppressor. grid ll connects to point in circuit with cathode 2, while'suppressor grid I'I' connects to point 24' in circuit with cathode 2'. Balanced operation of each circuit is obtained by adjustment of the power supply circuit through resistor 20, and by adjustment of resistors 1, Band 23, and 8 and 23' to those values to givepreferred characteristics of the tube and circuit for balance and best operation. Ahigh degree of stability is obtained and operationof the amplifier circuit effectively controlled.

I have heretofore described the balancing of coupled stages when each stage is balanced separately. .It isnot necessary to balance each stage separately, that ,is'the first stagecan serve'in its entirety as a unit affecting the tube circuit characteristics of the second stage and then the second stage can be balanced in the usual .way for maintaining zero output with zero input for varying power source potentials. Under these conditions the grid bias on: the second stage changes with thepower'source' voltage change similar to the way it changes in the first stage where the current change in resistor 1 produces a bias change.

With certain tubes balance of both stages may not be possible separately but the two stages as a unit invariably can be balanced as a high degree of flexibility has been introduced into the system with the introduction of' another tube. The grid bias on the second stage can thus be made to vary any desirable way giving as much negative slopeto the characteristics between the current in the balancing mesh of the last stage as is needed. The twintubes employed in the circuits of Figs. 4 and'5 show, in addition to other advantages, thatthe same elements can serve simultaneously to balance and amplify.

In Fig. 8 an, amplifying circuit of my invention is shown in which the output is balanced and this balance maintained by the dual compensatingaction of the circuit with power source changes and independent changes in the emission of the cathode other than those due to that of the power source. The tube shown is a diodetriodewith a filament cathode 2, control grid 3, triode anode 4 and diode anode 5. In normal operation the power source I9 is connected in series with the regulating resistance 20, adjustable resistors 8 and 23, the filament 2, switch 53 in a position and adjustable resistor I. When adjustment for change in emission compensation is-made, switch 53is thrown in'b position and resistances and 49 are adjusted so that the same current goes through resistors I, 23 and 8, but less through the filamentthan when the switch is in the a position. The input is connected between the end of resistor I and the control grid 3. The grid bias, due to drop in resistor 1, is maintained on the grid through a closed path in the input circuit. Adjustable resistor 9 is connected between anode 4 and one end of resistor 8, while the other anode 5 is connected to the other end of resistor 8 through adjustable resistors 50 and 43. The output is taken from anode 4 and the connection between resistors 50 and 43. Resistors 8, 9 and 43 form a three-resistance balancing mesh with the output. The resistances I, 8, 9, 43. 23 and 50 are determined experimentally and by calculation. as explained later, to give tube circuit characteristics that will give balanced and dual compensating conditions. The final adjustments are made in the resistances so that both a change in adjustment of resistor 20 and a shift of switch 53 from position a to position produces no change in the reading of a meter placed across the output connections. While adjusting for balance and compensation, the input is turned off.

Fig, 9 shows the same circuit as Fig. 8, adapted to a diode-triode heater type of tube.

Fig. 9a shows an alternative arrangement of the heater circuit which can be used when the power transformer has good voltage regulation. With the arrangement shown in Figs. 9 and 9a the final adjustments are made in the resistances so that there is no change in the reading of a meter placed across the output, both when resistor 45 is adjusted and the voltage on the primary of the power transformer is changed.

Fig. 10 is a circuit similar to that shown in Fig. 8 except that space charge grid [6 is used in place of the diode anode 5. The adjustments and operations of this circuit and this tube are similar to those stated for that shown in Fig. 8.

Fig. 11 shows the circuit illustrated in Fig. 1 arranged for balancing and dual compensation. Similarly to the circuit illustrated in Fig. 8, resistors 8, 9 and I4 form a three-resistance balancing mesh with the output. The balancing and dual compensating conditions are found in a manner similar to that described for Fig. 8.

Fig, 12 shows a further modification of my invention in which balance and compensation for both changes in the power source and changes in the emission of the cathode, independent of the power source, are obtained at the output by means of a circuit using a fourresistance balancing mesh at the output. A diode-tetrode is shown with filament cathode 2, tetrode anode 4, control grid 3. screen grid I8. and diode anode 5. The circuit is an extension of the circuit shown in Fig. 11 in that in place of one of the terminals of the output being from the connection between resistors 8 and 23, this connection is connected to the screen grid through two adjustable resistors and 50 in series, and this terminal of the output taken from the connection between resistors 50 and 5!. In this circuit the currents of two elements besides that from the principal anode are involved in the balancing mesh and, as is shown later in the theoretical discussion gives still more flexibility by allowing balance at zero potential on the output, when the input is off. to be maintained with both changes in the power source and independent changes in the emission for large ranges of characteristics of the tube cirdiode-triode shown in Fig. 11.

cuits. In this circuit the values of all the resistances of the circuit are determined by a combination of experiment and calculation to give best operating conditions and tube circuit characteristics that will balance. Final adjustments are made on resistances 8, 9, l4 and 5| so that no change in a meter placed across the output is produced when resistance 20 is adjusted and switch 53 is thrown from position a to position b.

Fig, 13 illustrates how circuits of the class shown in Fig. 8 may be cascaded. The elements of the second stage are designated by the corresponding primed reference figures. Adjustable resistor 22 enables a lower anode voltage to be used on the first stage than on the second stage, while adjustable resistor 55 enables additional flexibility to be obtained. Resistor 49 across the filament of the first stage enables less current to be used in filament of the first stage than in the second and takes care of the current through resistor 22 not passing through the filament of the second stage. The first stage is balanced so that a constant bias is maintained on the grid of the second stage with change of both cathode emission and power source. The resistors of this stage are determined for the preferred characteristics and best operation, and then the resistors 8, 9 and 43 are adjusted until the balance and dual compensating conditions are obtained. This is discussed further in the theoretical discussion. The balance and dual compensating condition is obtained on the second stage in a manner similar to that explained for Fig. 8.

In Fig. 14 is illustratedhow circuits of the class shown in Fig. 11 may be cascaded. The discussion above on Fig. 13 also applies to this circuit.

In Fig. 15 a circuit of the class shown in Fig.

, 10 is coupled with a circuit of the class of Fig 11 except that a twin-triode is used in place of the The extra grid 25, however, only serves to give greater flexibility to the tube circuit characteristics of the second stage. This grid obtains its bias from the drop in resistor 55 but does not function in the amplification other than its effect on the characteristics. The operation of this circuit is similar to the circuit of Fig. 13 except that similar to the circuit of Fig. 14, the output is taken from points of lower potential than that of the circuit of Fig. 13. The same explanation for balance and dual compensation given for the circuit of Fig. 13 applies here.

In Fig. 16 it is shown how the circuit of Fig. 15 is adapted to similar heater types of tubes.

In Fig. 17 it is shown how the circuit of Fig. 14 is adapted to heater types of tubes. The first stage is exactly similar but in the second stage a twin-triode is used in place of the diode-triode of Fig. 14. However, the two circuits are similar. The extra grid 25' obtains its grid bias from the drop in resistor 55 similar to that of the circuit of Fig. 15. Aside from the greater flexibility it derives by having this grid, it is the same type of circuit as that illustrated in Fig. 14 and functions similarly.

In Fig. 18 is shown another modification of my invention in which a four-resistance balancing mesh, similar to that of Fig. 12, is used to obtain the dual compensation. A diode-triode with two diode anodes l0 and II is shown. The currents of these two anodes are involved in the balancing and dual compensation. This circuit is also an extension of that of Fig. 11, where anode 10 corresponds to anode 5, anode H is connected to anode 10 through adjustable resistor 51 and the output terminal is then taken from anode H instead of from the connection at [2, as in the circuit of Fig. 11. All of the explanation given for Fig. 12 applies to this circuit except that in this circuit resistor 51 replaces in the balancing adjustments. The theoretical discussion of this circuit is given later and differs slightly from that of Fig. 12. This circuit has the advantage of having the output taken from points of relatively low potentials.

In Fig, 19 is shown a still further modification of my invention in which a four-resistance bal ance mesh, similar to that of Fig. 12, is used to obtain the dual compensation. This circuit s an extension of the circuit shown in Fig. 8 where the diode anode 10 replaces 5.- The extension comes in by connecting the additional diode anode H to the connection between resistors 43 and 58 through adjustable resistors 56 and 58 in series and taking the output from the connection between resistors 56 and 58 instead of between resistors 43 and 50. tion given for Fig. 12 applies here, while the theoretical discussion is the same as that for Fig. 18.

In Fig. is shown how the circuit illustrated in Fig. 18 is adapted to a triode-pentode tube. i

For balancing and compensation the triode anode 5 replaces one of the diode anodes 10,, and screen grid l8 replaces the other diode anode H of Fig. 18. The pentode suppressor grid I! is connected directly to the cathode. input is placed on triode control grid 80 and pentode control grid 3, the combined amplification is obtained in the output by the reactances of resistors I4 and 9. This circuit functions simultaneously to give twin amplification, balance and dual compensation.

Fig, 21 shows a still further modification of my invention in which balance and dual compensation are obtained. A diode-pentode is illustrated with filament cathode 2, control grid 3, screen grid [8, suppressor grid I1, pentode anode 4 and diode anode 5. The series circuit through the cathode and power supply 19 is the same as thatfor Fig. 12. Anode 4 in this circuit is connected to the connection between resistors 8 and I;

23 through adjustable resistor 5|. Anode 5 is connected to positive terminal of the power supply through adjustable resistor 9 and screen grid I8 is connected to anode 5 through adjustable resistor M. The output is taken from the pentode anode 4 and screen grid I 8. Resistors l4, 8, 9 and 5| form a four-resistance balancing mesh at the output. The same theoretical discussion and explanation as given for Fig. 12 applies to this circuit also.

Fig. 22 illustrates a two-stage, balanced, dualcompensating circuit in which the first stage is the same as the first stage of that of Fig. 15, while the second stage is an extension of that of Fig. 15 to a four-mesh balancing circuit. The tubes of this circuit are of the heater type and a triode-pentode in the second stage of this circuit replaces the twin-triode of that of Fig, 15. All the explanation and theoretical discussion given for the first stage of Fig. 15 applies to the first stage of this circuit. The extension in this circuit is that in place of taking one of the terminals of the output from the connection between resistors 8 and 23 the screen grid is connected to this connection through resistors 5i All of the explana- If the same These show the principles of my invention and and 50' and the output taken from the connection between 5| and 58'. The suppressor grid 11 is connected to the cathode. The explanation given for the circuit of Fig. 12 applies to the second stage of this circuit where resistor 5! corresponds to resistor 5|.

Fig. 23 illustrates a two-stage, balanced, dualcompensating amplifier with a diode-pentode arranged in a circuit like that of Fig. 18 for the first stage, and a second stage similar tothat of Fig. 22. The extra screen grid l8 in this circuit, which is not in that of Fig. 18, is not in the fourresistance balancing mesh. This is accomplished by paralleling resistors 8 and 23 with adjustable resistors 59 and 60, and then connecting grid I8 through resistance 50 to the connection between 59 and 68. With this arrangement there are two independent balancing meshes, the v four-resistance balancing rnesh, with resistances 8, 9, l4 and 51, which are balanced to maintain a constant grid bias on the next stage, and the tworesistance balancing meshwwith resistances 1 5i and 59, which is independently balanced to maintain a constant positive potential on the screen grid. The resistances of the first stage circuit and the potential forthe screen grid are determined by experiment and calculation so that the preferred characteristics and best operating conditions are obtained. The final adjustments are made in resistors 8, 9, I4 and 51 so that a constant grid' bias is maintained, on the second stage, with an adjustment of and thevol-tage regulator on the primary of the power pack transformer when the input is .turned 01T. A theoretical discussion of this is given later. The input is then turned on and 58 and 68 adjusted until thedesired constant voltage is maintained between the cathode and grid l8, with change in the input. The theoretical discussion of this two-resistance balancing mesh is also Fig. 24illustra tes a two-stage amplifier, each stage of which has two balancing meshes in which, together, they compensate for three variations. A space charge tetrode pentode is used i'n'the first stage with the same circuit as that shown in Fig. 23, where space charge grid l6 replaces anode. II. All the explanation given for the first stage of'Fig. 23 applies to this first stage. This has the additional advantage of giving combined amplification withinput on control grids 3i! and 3, while simultaneously compensating for power source changes and cathode emission at its output, and so that input does not change the screen" grid voltage. The second stage is the same as the first stage of Fig. 23. All of the explanation given for the first stage of Fig. 23 applies here except that the balance is maintained at zero when the input is turned ofi of thefirst stage of, this circuit.

I have shown certain two, three, and four-resistance balancing meshes and several combinations of thesewhere a single power source is used.

some of the Ways in which it canbe applied. These principles can be applied in many other ways. p

In Fig. 25 I have shown an independent source 74 for supplying the cathode heating current for the cathode 2 and also for securing the bias potential for control grid 3. An independent source 15, with regulating resistor 28', is employed for furnishing the plate potential. Adjustable resistors 88 and 9 are arranged in a two-resistance balancing mesh as shown. These two resistors are adjusted until a change in resistor 20' produces no change in the reading of a meter between the cathode and anode. By this means a constant voltage is maintained on the plate when the power source changes. The theoretical discussion of this circuit is given later. The cathode emission change due to variations of power source 14, is compensated for in the usual grid bias method by the variation of the voltage drop in resistor I. This shows the application of the compensating principle of my invention to holding triode amplifiers constant with variable power sources.

In Fig, 26 is illustrated the principle of my invention applied to maintaining constant potentials on both the anode and screen grid 11 of a pentode. The circuit is similar to that of Fig.

25 except that an independent provision is made to maintain a constant potential on the screen grid with the variation of the power source. For this, adjustable resistors 8 and 23 are shunted across 80 and the screen grid connected to their junction through resistor 43. Resistors 43 and 23 then are adjusted to compensate for the power source change so that a constant potential is maintained on the grid. For tubes in which the screen grid potential and. plate can be the same the output between the screen grid and plate can be used for D. C. amplification or direct coupling. Resistors 8, 9, 43, 23 and 80 can be so adjusted to maintain the same potential on both grid 1'! and anode 4 with change of power sources with the input off. The output variation will be proportional to the input and independent of the power source changes. As an A. C. amplifier with capacitance or other indirect coupling the preferred voltages on the screen grid and anode can be maintained and the output between the oathode and anode is preferred.

In Fig. 27 an amplifier is illustrated in which a tube similar to that of Fig. 26 is used which, in addition to the cathode 2, anode 4, control grid 3, screen grid 11, suppressor grid 78, contains a space charge grid 76. The space charge grid, with the cathode, acts as an emission source. The emission from this source is maintained constant with power source and other changes by adjusting resistors 1, BI, 82 until no change occurs in the emission when both switch 53 is thrown from position a to position b and resistor 28 is adjusted. The anode-screen grid part of the circuit is the same as that illustrated in Fig, 26 and all of the explanation given for the 1 circuit of Fig. 26 applies to this circuit.

Fig. 28 illustrates the circuit of Fig. 27 ap plied to a similar heater type of tube.

Fig. 29 is another variation of the circuit of Fig. 26.

In Figs. 1, 2, 3, 4, 5, 6 and 7, the output, with resistors 8, 9 and I4 form a circuit mesh which is to be balanced. Consider the potential drop across resistance I4 as E, the resistances 8 and 9 as R1 and R0, respectively, and the currents in R1 and R0 as I1 and I0, respectively. The factors affecting the balance of the bridge are the currents I0 and I1. These currents are each dependent on a common factor, which is the source of potential of the system, and the effects thereof may be made to neutralize each other for any variations in the potential source by properly adjusting the resistance of the circuit.

It will be appreciated that the same principles are involved in both a direct heated cathode circuit device, and the indirect cathode heating system as long as all power is obtained from the same source. There is a simultaneous change in the heating of the cathode, and the plate potential under conditions of changes in the common power supply. Accordingly, variation in cathode emission due to variation of power supply in the circuit shown in my invention will be balanced similar to the direct heated system.

The values of the two resistances 9 and 8 represented by R0 and R1, respectively, depend upon the characteristics of the tube and circuit. The simplest way to determine this dependence is to regard the output circuit across resistance I4 as having. a voltage drop designated E, and the re sistances R0 and R1 as a Dowling zero shunt. When a current I0 is passing through R0 and a current I1 through R1, then the requirement for no current through the output circuit is:

Now for the circuit to be balanced for a change A10 in IQ and a corresponding change A11 in I1, the following equation must hold:

The above is the value of R0 for balanced conditions in terms of E, I1, In and the slope of the I1 vs. Io characteristics. R1 is then determined by Equation 1. 7

If E, the voltage drop across resistance I4, is constant and it can be considered as a first approximation as constant, because the effect on it of a change in electron emission is counteracted by the effect on it of the change in potential drop across resistance 23 caused by a simultaneous change in I1, it is evident that the characteristics must be such that the denominator is a constant for all values of In in order that Re can be a constant. By putting the denominator in diiferential form equating it to a constant and solving the differential equation, we obtain the characteristics of I1 vs. Io necessary to have R0 a constant as follows:

Equation 5 is the general equation of a straight line. Therefore, if the portion of the characteristics near th operating value of In is straight, the circuit will balance and remain balanced.

The length of this straight portion determines the range of external fluctuations that can be balanced. This requirement is usually fulfilled for normal operating conditions. This one-tube circuit afiords so simple a means of balancing external tube variations that it is as easily set up as an unbalanced circuit, will operate much more satisfactorily, and. with refinements, will balance as closely as the two-tub circuit. The advantages over the two-tube circuit are: the elimination of the difliculty in balancing, of extra apparatus, and of the necessity of obtaining exactly similar tubes, which are not readily procurable.

The balancing by adjusting resistances R0, R1, and voltageE. Without voltage E, the circuitwould not balance even though it appears the drop RoIo could be made to balance drop RlIl. This is not possible, as can be seen by allowing E to equal zero in the first equation after Equation 2, which will then cause R to cancel out of the equation and thereby eliminate the means of adjusting for balance. To have a voltage drop E in the circuit R0, R1, and the output, is an essential feature of the circuit of my invention. a

The actual values of the resistances R0 and R1 need not be calculated from Equations 3 and 1, but can be determined xperimentally as follows: A suitable D. C. electric current meter is placed across the output terminals with R0 not far from the expected correct value and R1 is adjusted until the meter reads zero. The supply current isthen increased by increasing the voltage into th supply circuit and the deflection of the meter noted. Then, with a new value of Re (a value which differs from the expected correct value in the opposite direction from that of the first value taken), R1 is again adjusted for zero reading of the meter, and the deflection of the meter again noted for an increase in supply current. If the correct value of R0 for balance is near the'value which was expected, this second deflection will be in the opposite direction to the first. Values of R0 between these two are then taken and the above procedure repeated until a value of R0 and R1 is found for which no deflection is produced in the meter when thesupply current is changed;

Every tube even of the same type and make differs,

enough in characteristics to require the values of R0 and R1 to be determined experimentally for balance against supply power changes.

The assumption that E- is constant is introduced to simplify the discussion and to show the fundamental idea of balancing against changes in supply power. Actually, the assumption of E being constant is an unnecessary assumption and can be replaced by the assumption that the resistances I4, 9 and 8 remain constant which can always be accurately fulfilled. v I

Th following discussion. will show that the circuit of my invention will balance, not approximately, but completely for normal operating voltages on the tube and that the conditions are not altered from those just given, [4 being any suitable constant resistance, and R0 and R1 determined experimentally in exactly the same 'way' as before. Call resistance It, R2; and the current through it, I2. Then, for balance at some current In with the corresponding currents I1 and I2, the following equation must hold:

Io+AI0 causing I2 to change to I2+AI2 and I1 to I1+AI1, the following equation must hold also:

R0(I0+AIo) +R2I2+R2AI2=R1Q1+AID substituting R0 in this, gives in these circuits is accomplished;

Now to remain balanced when Io changes to Cancelling and rearranging, gives R1(I1AIo-IOAI1)=R2(IzAIo-IOAI2) A1 1fi I AI I AI ZT R LAID-1 M, I I A I 1 (7) 1 AI k This is a similar condition to that of the previous case, the denominator having exactly the same form. Here, the numerator also has exactly the same form. In order for the denominator to remain constant with change of In and I1, it was shown that the only requirement was that the I1I0 characteristics must be linear in the operating region, so here in orderthat the numerator remains constant with change of I0 and I2, the I2Io characteristics must also be linear in the operating region. These twoconditions are practically always met in amplifying tubes.

As it is the ratio that must fit the requirement of the character istics of the tube given by Equation '7, the resistance R2 can be chosen arbitrarily within the operating range and R0 and R1 determined experimentally in exactly the same way as indicated in the simplified discussion.

If, in place of solving first for R0 in Equation 6, R1 is obtained as follows:

and then it is eliminated in place of Rathe second condition of balance,

. 10 o IM-IFATL I (g) 114 is obtained. i

From this, it is seen thatRn can just as well be chosen arbitrarily in place of R2 and then R2 and R1 adjusted for the balance conditioniexperiment-ally in exactly the same way asR a'rid- This is a more convenient method of adjusting, as during adjustment, the tube can be held closer to its operating voltages. -As R0 is arbitrary, a special case of this circuit is when R1 were.

So far, it has been shown that these circuits will completely balance out changes'in the supply power sources. It will be shown now that further adjustments of these circuits of my invention are'possible, whereby the circuits will balance both changes in the power ,source, and changes iii-cathode emission due not only to variations in the power supply, 'but to any cause, as for example, the deterioration of the cathode i or filament.

To compensate for cathode emission change This is accom-- is emitting less electrons or the switch 53 is in position b; the s and S should be adjusted so that 1 1 1 s+h' *h This is accomplished experimentally for any desired decrease in emission by merely adjusting S and s so that the meter 5 will read the same with the switch in position b as it did with the switch in position a. With this adjustment the emission is changed but the resistances of the circuits, except those of the tubes changed by the emission, remain constant. This is a means of producing a change in cathode emission independently of the power source change. Therefore if the tube is balanced so that there is no change in the output when switch 53 is thrown from position a to position b the tube, when being operated normally i. e. with switch in position a, will remain in balance if the cathode emission changes for any reason whatsoever.

An alternative way of securing this independent change of emission for heater types of tubes when the voltage regulation of the power transformer used in the power pack is good, is merely to adjust resistance 45 shown in Fig. 9a.

The voltage of the power source is changed to obtain adjustment of the circuit for balance of no change in the output when the power source changesby adjusting resistance 253 for filament type of tubes and by adjusting any kind of voltage regulator before the power transformer for heater types of tubes.

It is by these means possible to make independent changes in the electron emission of the cathode and the voltage of the power source. I will designate this variable emission property of the cathode by the variable X and the voltage of the source by variable E. These two variables are independent and effect all the currents in the tube circuit. It is to be noted that both E and X change the cathode emission and in general all the currents and voltages of the circuit, but that each functions independently.

Resistances 8, 9 and 43, in Figs. 8-10 and 13 and the first stages of Figs. 15, 16 and 22, and resistances 8, 9, and M, in Figs. 11, 14 and 17 and the second stages of Figs. 15 and 16, together with the output, form a mesh of the circuit that is now to be balanced for no change in output when both independent changes of electron emission properties of the cathode and changes of power voltage source are made. The resistances 8, 9, and 43, and 8, 9, and I4 and the corresponding primes, may be designated R1, R0 and R2 respectively and the corresponding currents ii, 2'0 and 2.

The conditions for balancing when only the power source changes are discussed above and in the parent application Serial Number 732,170, filed June 23, 1934, now Patent 2,166,184, and show that for proper adjustments the balance will hold in the linear part of the tube circuit characteristics. It was also shown by experiment that such characteristics as i1io are linear through a large range of values. We will consider now the conditions for balance for the linear part of the tube circuit characteristics. This discussion will therefore hold in general, the only limitation being on the range of variation of E and X for which the circuit will remain balanced. It is found that with some tubes a high degree of balance can be maintained over a range of variation of better than The equations for the currents are then of the form i=a+nE+mX or specifically which are equations of tube circuit characteristics.

' Di 0 i =n and 121 so the ns are the partial derivatives with respect to E and X respectively.

The total change in any current is given by The corresponding equation for change of X is (3) R0 di0 E+R2 di2 E R1 di1 E By substituting the values of the (dihps and (dime and cancelling the dEs and dxs respectively, Equations 2 and 3 become Putting in the values of 2'0, i1 and i2 in Equation 1 it becomes Multiplying Equation 2 by E and Equation 3 by X, adding them together and subtracting their sum from (1) gives This equation, together with Equations 2 and 3, gives the independent equations of this circuit mesh for the conditions sought.

aoRo-I- d2R2-(Z1R1 0 7ZDRO+7L2R2 1L1R1 0 moRo-fmzRz m1R1: 0

This is a set of linear, homogeneous equations which only have a solution if the determinant of the set of equations is zero, or

The tube circuit characteristics are given by the values of these ws, his and ms. The above equation indicates the requirements of the tube circuit characteristics that must be met in order that the circuit can be balanced for power supply voltage change and change in cathode emission properties. These characteristics can be varied by adjusting 7, 20, 23, and the actual power supply voltage. When this requirement of the characteristics is met then for any given value of R1, the correct values of R0 and R2 can be calculated from any two of the equations as follows: a

This same analysis holds for circuits, Figs. 1, 2, 3, 4, 5, 6, 7 and all the circuits in the parent patents with three-resistance balancing mesh, if resistances 48 and 49 and switch 53 are inserted in the circuit.

All these circuits can then be balanced for both change of emission properties of v the cathode and change in power supply voltage ii the characteristics of the tube circuit are obtained experimentally and then varied until holds. The desired.- value' of R1 (that which gives a sufficient amplification) being used, the correct values of R and R2 are thencalculated fromthe above equations. The final adjustments can be made experimentally by making slight adjustments of the'various resistances until no change in the outputoccurs witheither a change of 53' from a to b or with an adjustment of the power supply voltage. v

' It is to be noted 'that' a set of linear homogeneous equations is formedbecause we are ba1- ancing for zeroand have just as many resistances in the balancing mesh as we have independent conditions. When a set of homogeneous equations is obtained, then balance for all changes can only bepbtainedwhen the circuit is adjusted so that a definite relation between the tube circuit characteristics'i s obtained. Any change in the conditions required that will produce a set of linear equations any one of which is non-homogeneous will remove the requirement of a definite relation between the tube circuit characteristics and therefore allow balance for a large range of desirable characteristics merely by adjusting the three resistances in the balancing mesh.

In Figs. 13, 14, and 15, when each stage is balanced separately, the circuits for the first stage must be balanced so that a constant negative bias for the second stage is maintained on the output of the first stage. This requirement makes the first equation non-homogeneous. That is, Roz'o+R2i2 R1i1-=eiwhere e 'iS positive in Fig. let and negative in Figs. 13 and '15. There is no change in the compensating equations so the three independent equations are: v 1

This. setof equations has a unique solution if 7 t z i W 77,2 77/1 m 1722 m So this stage can-be balanced for any relation circuit currents characteristics.

between the characteristics except the onethat was previously required for zero. The solution of these equations is E ("0 a e) This same analysis holds for any second stage also if it is not undesirable to-have a fixed constant potential superimposed on the output. For A. C. amplification this is not objectionable and in some D. C. amplifiers.

This same analysis holds for all three-resistance balancing mesh circuits shown in this patent and the parent patents if the provisions ror adjusting for cathode emission properties as indicated in this patent are made in the circuits. Any tube circuit with at least a threeresistance balancing mesh shown in this. patent or the parent patents can be coupled with any other such tube circuit and each stage separately balanced for both these changes.

The importance of the tube circuitcharacteristics is shown in this discussion. The way the circuit shown in Fig. 15 is arranged enables large flexibility in the characteristics of the current from the auxiliary balancing element of the second stage to be made. The negative potential on the grid 25 can be varied quite arbitrarily and so can be adjusted that any necessary characteristics to effect balance can be obtained. It can readily be seen that with such a circuit, adjustment of 55, which is quite arbitrary, will make it possible to meet the requirements for zero potential to be maintained on the output with almost any tube when no input isimpressed on the first stage.

Referring again to the set of homogeneous equations set up from the three-resistance balancing mesh, when balanced for zero output with zero input, it was shown that the set would be made non-homogeneous by changing the requirements to a balance fora constant voltage 6 across the output. When the set of equations is nonhomogeneous thenbalance is possible without a definite relation between the tube circuit characteristics. Now if it is desirable to get this double compensating condition and still have a balance for zero voltage across the output, it is necessary to introduce an additional current and resistance in the balancing mesh of the circuit. Any fourresistance balancing mesh will give the flexibility desired so that a balance for both the power source voltage variation and cathode emission property variation can be effective for the maintenance of a zero voltage on the output independent of a definite relation between the tube With such a tube circuit, resistances other than the resistance in the balancing mesh, together with the voltage, are adjusted until the desirable characteristics are obtained and then the resistances of the balancing meshadjusted until thebalanced condition is obtained. This result is indicated mathematically by using an equation in which the sum of the voltage drops across all the resistances in the balancing mesh is equated 'to zero. This equation, together with the two compensating equations, form a set of non-homogeneous linear equations for which'there isa unique solution of three of the resistances in terms of the fourth and the tube circuit characteristics.

Circuits with four-resistance balancing meshes are shown in Figs. 12, 18, 19, 20, 2 1, 22, 23 and 24. In Figs. 12 and 21 andthe second stages of Figs. 22 and 23, consider 9, 8, l4 and 5|, in Fig. 19, consider 9, 8, l4 and 56 and in Figs. 18, and 24 4 and the first stage of Fig. 23, consider 9, l8, l4 and 51 as resistances R0, R1, R2, and R3 respectively, and i0, i1, i2 and is as thecorresponding currents. For balance i0R0+i2R2=i1R1+i3R3.

and similarly as before we obtain fromthese equations the three independent equations This is a set of non-homogeneous linear equations, and they have a unique solutionif More particularly, in Figs 18, 20, 23 and 24, resistors 9, 8, l4 and '51, and in Fig. 24 resistors 9', 8, l4 and 51', may be designated R0, R1, R2, and R3 respectively and the corresponding currents through them in, i i2 and Then similarly as above We have Ruio' 'Rzi2+Rsia=Riii and the three independent equations are The tube circuit characteristics, that is the as ns and ms of the circuits, are obtained experiment-ally for the preferable values of all the resistances of the circuit except 8=R1, R2, and 5|, 56 or 5=l=Ra and then the values of these resistances are determined from the above equation. The final adjustments are made experimentally by slight adjustments until the exact values at which a change in E and X will produce no change in the output. A four-resistance balancing mesh compensating for changes of power-source voltage and cathode emission properties and maintaining a constant voltage on the output with zero voltage on the input, is a similar condition to the case of maintaining zero voltage on the output. If a voltage e is to be maintained on the output of any stage which is to produce the grid bias for a secondstage when the input is zero, as for example the first stage of the circuits of Figs. 23 and 24, then the balancing equation will be R0i0+R2i2+Rsi3=R1i1+e and Equation 1 will be (1) a1R1+a2R2+a3R3=eaoRo The compensating equations will not change so the solution willbe D has the same value as before. The solution for the other type or four-resistance circuit would be similarly changed for this condition.

Multiple stage amplifiers can be formed out of any combination of any four-resistance balancing mesh circuits and .a separate power-source used for each stage or the same power-source used for any combinations of stages. The complete compensation of E and X changes can be adjusted for in each separate stage as described above, since all four-resistance balancing meshes for any condition of balancing fall into one of the four above cases.

Further, multiple stage amplifiers can be formed out of any combination of any three or 

